The present invention relates generally to container ends and more particularly to an improved end for a pressurized container and method of forming such end.
Because of the very large market for beer and beverage cans and the very competitive pricing of such containers it is important that such cans, including their ends, be made as economically as possible. A significant portion of the manufacturing cost of such ends is represented by the metal. As is well appreciated by those skilled in the art, even a minute metal saving in each end may result in millions of dollars in savings to the can industry due to the billions of ends produced. Therefore, a relatively small reduction in the thickness of metal while maintaining the strength of the end is of significant economic importance. Conversely, an increase in strength using the same thickness of metal is also of great importance.
The configuration of ends conventionally used to close drawn and ironed beer and beverage cans comprises a central panel surrounded by a generally U-shaped sidewall integrally joined to the central panel by a convexly curved intermediate section. The outer leg of the side wall is provided with a reverse curl at its upper end which is double seamed onto the flange of the container. After seaming the outer leg is substantially parallel with the sidewall of the can while the inner leg of the sidewall is disposed inwardly at an angle.
It has been recognized that having the two legs of the U-shaped sidewall substantially vertical and increasing the panel height increases the buckle strength of the end. Thus in U.S. Pat. No. 4,217,843 there is disclosed tooling for forming the sidewall in such a manner that the legs are more nearly vertical and the panel height is greater than was previously the case. It is also known that doming the central panel provides increased buckle strength. As shown in U.S. Pat. No. 4,217,843 this is normally done at the last forming station for making can ends by tension stretching the panel portion of the end with a doming tool having the desired radius of curvature. Other doming techniques proposed include that shown in U.S. Pat. No. 3,441,170 where the curved segment connecting the inner leg of the sidewall to the central panel is coined on the undersurface. This is for the purpose of reducing the metal thickness in the intermediate segment to the point where it functions as a hinge thus enabling the panel portion to dome as a result of the pressure of the contents of the can. Coining the undersurface of the curved segment but approximately to a lesser depth is also taught in the aforementioned U.S. Pat. No. 4,217,843 for the purpose of work hardening and thus stiffening the segment.